This invention relates to an electronic apparatus responsive to input signals for repetitively actuating an output device for testing the apparatus and the output device. More particularly, this invention relates to a modification to a calculator or microprocessor, in which the calculator or microprocessor is responsive to input signals for repetitively actuating an output device such as a printer when the calculator or microprocessor is placed in a test mode.
Electronic microprocessor or calculator integrated circuits are frequently used with output devices, such as thermal or mechanical printers, visual displays, typewriters and the like. During the manufacturing process for such equipment it is desirable that the output devices, as well as the integrated circuits, be tested to assure proper operation thereof before the equipment is delivered to the ultimate purchaser. Electronic calculators, and especially electronic printing calculators, are preferably tested while still in the manufacturers plant. The testing may include a "burn in" test, that is, a test over a prolonged period of time, because electronic components sometimes fail not immediately, but rather after a short period of operation. Electronic printing calculators utilizing thermal printing units may fail not immediately but rather after several minutes to several hours of operation. Thus, such electronic printing calculators are tested over a prolonged period of time, usually 24 hours or longer.
To conserve the amount the paper tape used this "burn in" test is generally accomplished by intermittently actuating the calculators' printer units rather than by continuously printing during a long period of time. Originally this testing was manually performed by employees of the manufacturer of the calculator who would periodically cause each calculator tested to print out a line of characters. Subsequently, in order to lessen the amount of human labor involved, racks were provided for testing the calculators, the racks being provided with power supplies for the calculators (if required) as well as two or more electrical contact pins for each calculator to be tested. Preferably, the bottom case of each calculator was provided with a connector mating with the contact pins on the rack; the contacts in the calculators' connector were coupled to the calculator's keyboard and the contact pins on the rack were coupled to one or more switches or relays. The connections were arranged such that when the switches or relays were closed (in the proper sequence, if need be), the calculators were caused to print a line of characters (such as a line of the numeral eight). By providing appropriated timing apparatus for periodically closing the switches or relays, the calculators installed in the rack would intermittently perform the desired printing operation. While this equipment overcame inefficiencies involved with manual testing the calculators, it raised other problems, such as (1) the manual labor associated with requiring each calculator tested to be mated with the pins on the test racks, (2) breakage of either the pins or calculator connectors during use of the test rack, (3) the expense of the rack and testing apparatus and (4) the need to either standardize the test connectors or to alter the testing apparatus for a calculator model change.
It is therefore one object of this invention to eliminate the need for such special testing apparatus. It was another object of this invention that the calculators be easily tested without the need either for special connections between the calculator and some testing apparatus or for manual inputting of the line of characters to be printed for such printing operation. It was therefore another object of this invention that a calculator be provided with a self-testing mode of operation.
By eliminating the connections between the test racks and the calculators, the cost of test racks is significantly reduced, as well as the cost of maintenance thereof, the yield of calculators from an assembly line is improved and any need for redesigning the test rack upon changing the design of the calculator is avoided.
The foregoing objects are achieved as is now described. Microprocessor integrated circuits used in calculators and other equipment normally have an instruction word memory for storing a plurality of instruction words which are addressed by the contents of an address register. The instruction words read from the instruction word memory are decoded, such as by an instruction word decoder circuit, and are used to control the operations performed by the calculator in response to depression of keys at the calculator's keyboard. By loading the instruction word memory with appropriate instructions, the calculator may be made to perform many different and useful data handling and printing operations in response to different inputs at the calculator's keyboard. The microprocessor integrated circuit is caused to enter a self-testing program in response to appropriate input signals such as those caused by depression of a preselected sequence of keys at the calculator's keyboard. During the self-testing program, a memory in the microprocessor is loaded with a preselected multi-digit alphanumeric code and the preselected multi-digit alphanumeric code is automatically and repetitively transferred to the calculator's printing unit for printing thereat. Preferably, a timer circuit is also provided for timing period between printing operations, which period may be selectively controlled by an input at the keyboard; thus the timer circuit controls the rate at which the printer unit is actuated by the contents of the memory. Accordingly, the printer unit is repetitively and automatically actuated, the period of time occurring between actuations thereof either being a function of the data entered at the calculator's keyboard in one embodiment or being of a preselected duration in another embodiment.